This application claims the priority of German patent 198 38 452.1, filed Aug. 25, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a steering wheel for a motor vehicle having a steering wheel rim which is connected to a steering wheel hub by way of a supporting structure, in particular a spoke arrangement, in which case the steering wheel rim is provided at least in some places with at least one cavity which is open, through at least one ventilation opening to a gripping region of the steering wheel rim.
It is known for example from German patent document DE 37 13 450 A1, for the temperature of a steering wheel of a motor vehicle to be stabilized by heating or cooling. For this purpose, a steering wheel rim is part of a funnel-like supporting structure, with the entire supporting structure including the steering wheel rim being designed to be hollow. The casing of the steering wheel rim is provided with outlet openings all the way around for air at an appropriately stabilized temperature. The steering wheel has a relatively complex associated circuit for the temperature-stabilization medium.
A similar steering wheel for a motor vehicle is known from German patent document DT 21 64 976. A steering wheel rim is provided with a circumferential annular channel which is connected, at the level of two spokes, to supply channels which run through the spokes. The supply channels are routed in a casing tube, in which case the casing tube can be supplied via appropriate connecting lines with hot air taken from the engine compartment or with fresh air which is taken from the relative wind of motion and is sucked in via a fan.
The object of the invention is to provide a steering wheel of the type mentioned initially, in which it is possible to stabilize the temperature of the steering wheel rim in a simple manner.
This object is achieved in that in the region of the at least one cavity, the steering wheel rim has a holder for fixing a fan module which sucks in air from the vicinity of the steering wheel rim and passes it into the cavity. The invention is based on the knowledge that, owing to the airbag units which are fitted in modern vehicles, there is not enough space in the body of the steering wheel for a suitable practical configuration for known solutions for routing an air channel from the casing tube region to the steering wheel rim. By directly fixing the fan module to the steering wheel rim, there is no need for air supply channels since the fan module sucks in environmental air directly and passes it into the at least one cavity. In this case, environmental air is sucked in in the immediate vicinity of the steering wheel rim. The cooling effects of appropriate ventilation is provided by the gradual circulation of the air in the vehicle interior, in which case, owing to the flow conditions there, cooler air is also gradually sucked in out of the casing tube and footwell region of the vehicle interior in addition to the environmental air located in the immediate vicinity of the steering wheel rim. The solution according to the invention compensates for the disadvantages of poorer cooling air supply in the initial phase of ventilation in that the resistance to the air flow is considerably reduced owing to the lack of air supply channels. The steering wheel rim can be provided either with a continuous, circumferential cavity or else with cavities which are distributed in sections around the circumference of the steering wheel rim. The at least one ventilation opening is used as an outlet opening for the air supplied by the fan module, and such openings may have different flow geometries. Either a single outlet slot may be provided or, preferably, a large number of irregularly distributed outlet holes. The ventilation openings are preferably arranged only in the gripping region of the steering wheel rim, in which case the gripping regions represent regions where a driver normally grips the steering wheel.
In a refinement of the invention, the steering wheel rim is designed as a self-supporting hollow body structure. The preferably annular hollow body structure is designed such that the hollow body structure itself has sufficient stiffness and strength on its own. Wire inserts or struts, as are present in the steering wheel rim according to the prior art, are avoided in order to achieve good flow conditions with a continuous cavity within the steering wheel rim.
In a further refinement of the invention, the fan module is arranged in an attachment region of the steering wheel rim, at the level of a steering wheel spoke of the spoke arrangement. This is a particularly advantageous arrangement, since the fan module can be integrated in a space-saving manner in the attachment region (which is required in any case) of the steering wheel rim to the spoke arrangement. The fan module preferably has a small fan which is integrated in a tubular sleeve which has an outlet that opens into the cavity at one end as well as an inlet (which is in the form of an induction stub) at the opposite end in the flow direction. The fan module may be designed in a simple manner as a cylindrical tubular section, in which the fan is integrated with its rotation axis aligned coaxially with respect to the center longitudinal axis of the tube. The tubular section in the form of a stub is designed to be relatively short, and one end is embedded in the holder for the steering wheel rim, or is flange-connected to it in some other way.
In a further refinement of the invention, the steering wheel rim is produced with one or more shells from at least one metal sheet. The design of the steering wheel rim from at least one metal sheet allows the ventilation openings to be incorporated without any notches being produced which would lead to weakening of the material. For this reason, it is not directly possible to use metal castings. When using metal sheets, bending loads can be absorbed without the metal sheet failing. The steering wheel rim is preferably assembled from two sheet-metal half shells. However, it may also be formed with a single shell or from three or more shells.
In a further refinement of the invention, the steering wheel rim is formed by two half shells which are connected to one another, in which case a lower half shell is connected to the supporting structure and an upper half shell is provided with the ventilation openings. This refinement allows simple and cost-effective production. If the upper half shell were to be connected to the supporting structure, in particular to the spoke arrangement, then this would result in considerably increased manufacturing effort. The spoke arrangement may comprise a plurality of spokes, in manner known per se, in which case between two and four spokes are preferably provided. Since, in contrast to the prior art, the spokes have nothing to do with the ventilation system, the arrangement and number of spokes may be chosen as required, depending on other requirements such as stability or stylistic demands.
In a further refinement of the invention, the upper half shell is designed as an injection-molded plastic part. The connection between the upper half shell and a lower half shell designed as a sheet-metal part can preferably be provided by a latching or crimped connection. Furthermore, the two half shells can be mechanically connected to one another in a positively locking manner. Latching or crimped connections are particularly advantageous for use as positively locking mechanical connections, since no separate connecting elements are required for this purpose.
In a further refinement of the invention, the two half shells are connected to one another with an integral material joint. Suitable techniques for this purpose are, in particular, welding, soldering or bonding, in which case an appropriate weld can be produced using a circumferential weld bead, or else using spot welds.
In a further refinement of the invention, the steering wheel rim is formed by an integral metal sheet, in which case a joint line is provided on the external circumference of the steering wheel rim. The steering wheel rim is produced from an integral metal sheet by a rolling bending process about two axes, thus resulting in the desired, tubular structure. The joint line for those longitudinal edges of the metal sheet which are in contact with one another after the rolling and bending process is provided on the external circumference of the steering wheel rim. This reduces any risk of injury caused by impact of the driver's head. If the joint line were on the front face of the steering wheel rim facing the driver, this would result in a considerably greater risk of injury, if the longitudinal edges were to stand proud as a result of corresponding damage to the steering wheel rim, producing sharp cutting edges. Even when the steering wheel rim is formed from two half shells, the joint regions are respectively provided on the external and internal circumference of the steering wheel rim, so that the risk of injury on head impact is also reduced with this refinement.
The invention also relates to a method for producing a steering wheel rim for a steering wheel of a motor vehicle, which is provided with ventilation openings and is formed by a hollow body.
The object of the invention is thus also to provide such a method, which allows simple and stable production of a steering wheel rim with ventilation.
This object is achieved in that the steering wheel rim is formed by two metal sheets which are initially flat, in which case the ventilation openings are stamped in at least one metal sheet, the two metal sheets are then formed into corresponding half shells, and are finally connected to one another. A simple stamping process can be used to incorporate the ventilation openings in the flat metal sheet. If the ventilation openings were not to be incorporated until the metal sheet had been formed, then this would incur considerably greater production effort.
The object on which the method is based is also achieved in that the steering wheel rim is formed by an integral metal sheet, into which the ventilation openings are first of all stamped in the flat state and which is subsequently formed into a tubular structure by rolling bending about two axes, and is finally welded at the joint gap which is formed. The method according to the invention means that it is also possible to use an integral, flat metal sheet to produce a hollow body structure, and thus a steering wheel rim. Joining processes, in particular such as welds or crimped connections, are simplified by the presence of only a single, circumferential connecting joint (joint gap).